One of the greatest impediments to speed and efficiency for water borne vessels is the loss of energy created by water resistance. One form of this loss of energy is the wake generation which occurs as a vessel passes through the water; the greater the wake, the greater the energy loss. Reducing this wave making resistance is an important way to improve the performance of a vessel. In the past, two primary methods have been used to reduce this component of resistance in a partially immersed hull with a given weight and speed. The first has been to increase the effective immersed length of the hull. The second has been to reduce the amount of water displaced by the hull on a given immersed length by separating the immersed volume into multiple hulls.
In the past, hydrofoils have been used on sailing craft as a way of to avoid many of the limitations of partially immersed hulls traveling through water. Most of these craft have been configured such that their weight is fully supported by the dynamic lift on their foils.
In addition hydrofoils have been fitted to craft traveling with partially immersed hulls. In sailing craft they have been used to control fore and aft trim in boats with narrow hulls that have relatively limited fore and aft stability, such as multiple hulled craft and International Moth class single hulled craft. In these cases the hydrofoils have been mounted to the rudder(s)of the vessels at a fixed angle to the hull(s) of the craft. As the moving craft pitches forward or aft, dynamic lift on the foil acts to return the craft to its designed trim angle. These foils have always been mounted deeper than the proposed invention and have not been designed to significantly affect the wave making resistance of the hulls on which they are attached.
There remains a need for vessels with partially immersed hulls to reduce the energy lost to wave making resistance. In the case of powerboats, reduced resistance would result in reduced fuel consumption and/or increased speed. In the case of sailing craft, reduced resistance would result in greater performance.
I have discovered a mechanism to significantly reduce the loss of energy due to wave making as the partially immersed hull of a single hulled craft moves through the water. This invention employs a hydrofoil submersed aft of the stern of the vessel, located near the surface of the water and capable of significant lift upwards. The effect of the hydrofoil is to reduce the amount of wake generated by the vessel when traveling through water and thereby reduce the energy lost to wake formation. The effect is to increase the performance, relative to a vessel lacking such a hydrofoil, for a given amount of propulsion energy applied to the vessel.
In the case of vessels that travel at a wide range of speeds (such as most high performance sailing craft), this hydrofoil may be configured so that its angle of attack relative to the hull may be adjusted.
The invention features a hydrofoil device for reducing wake formation on a partially immersed hull of a single hulled vessel. The hydrofoil device includes a transverse hydrofoil positioned below the surface of the water when said vessel is in the water, said hydrofoil being capable of a positive angle of attack of between 2 to 8 degrees to the static waterplane. The hydrofoil device further includes a strut or multiple struts for attaching said hydrofoil to said vessel, a means for attaching said hydrofoil to said strut or struts, and a means for attaching said strut or struts to said vessel.
In various preferred embodiments, the hydrofoil has an adjustable angle of attack, relative to the static waterplane of the vessel; the strut is the rudder of said vessel; the hydrofoil device is attached to said vessel by a single strut; the edges of the said hydrofoil are curved and do not lie within a single plane; the positive angle of attack is between 2 to 8 degrees; the leading edge of the hydrofoil has a length which is between 5% and 15% of the immersed length of the vessel aft of the transom of the vessel; the upper surface of the hydrofoil is between 5% and 15% of the immersed length of the vessel below the static waterplane of the vessel; the hydrofoil reduces the wake formation of said vessel when said vessel is moving, relative to a vessel lacking said hydrofoil.
The invention also features a method of reducing wake by attaching multiple hydrofoil devices featured by the invention to a vessel such that the transverse axis of one of the said hydrofoils may be horizontal when the vessel is heeled. In a preferred embodiment each of the hydrofoil devices is supported (attached to the haul) via a steering rudder which serves as the strut, such that there are multiple steering rudders on the vessel.
In an additional preferred embodiment, the vessel is a sailboat and said hydrofoil device is mounted to a vessel by means of a track device that allows said strut to be moved relative to the vertical axis of the transom of said sailboat such that the transverse axis of said hydrofoil may be more horizontal relative to the waterplane when said sailboat is heeled.
In yet another embodiment, the means for attaching the hydrofoil to the strut is a rotating means for the purpose of adjusting the angle of attack of said hydrofoil; the hydrofoil is rigidly attached to said strut and the means of attaching said strut to said hull is a rotating means for the purpose of adjusting the angle of attack of said hydrofoil; the vessel is a powerboat; the vessel is a sailboat; or the presence of the device on the vessel allows a reduction of wake of at least 50%, relative to a vessel lacking said device when said vessel is operating in Froude numbers from about 0.3 to 0.5.
xe2x80x9cWaterplanexe2x80x9d means the plane defined by the surface of the water.
xe2x80x9cStatic waterplanexe2x80x9d means the waterplane, defined relative to the vessel, when the said vessel is floating stationary in calm water.
xe2x80x9cHydrofoilxe2x80x9d means a surface designed to efficiently produce dynamic lifting force oriented approximately opposite to the direction of gravitational force as the vessel to which it is attached moves through the water.
xe2x80x9cSpan of the hydrofoilxe2x80x9d means the dimension of the hydrofoil perpendicular to the direction of intended vessel motion and parallel to the waterplane of the vessel.
xe2x80x9cLeading edge of the hydrofoilxe2x80x9d means the edge of the hydrofoil closest to the bow of the vessel.
xe2x80x9cTransverse axis of the hydrofoilxe2x80x9d means the axis which both lies within the plane containing the edges of the hydrofoil and is perpendicular to the intended direction of water flow over the hydrofoil.
xe2x80x9cForwardxe2x80x9d means the direction of the intended direction of travel for the said vessel.
xe2x80x9cAftxe2x80x9d means the direction opposite to the designed direction of travel for the said vessel.
xe2x80x9cSternxe2x80x9d means the extreme aft end of the craft""s hull.
xe2x80x9cAngle of attackxe2x80x9d means the angle at which the plane of the hydrofoil intersects the static waterplane of the vessel.
xe2x80x9cPositive angle of attackxe2x80x9d means an angle of attack at which the plane of the hydrofoil intersects the static waterplane forward of the leading edge of the foil.
xe2x80x9cNegative angle of attackxe2x80x9d means an angle of attack at which the plane of the hydrofoil intersects the static waterplane aft of the leading edge of the foil.
xe2x80x9cStrutxe2x80x9d means a structural support which supports the hydrofoil in its position relative to the vessel.
xe2x80x9cRudderxe2x80x9d means a surface which is designed with the primary purpose of providing directional control to the said vessel.
xe2x80x9cPartially immersed hullxe2x80x9d means a hull that is intersected by the plane which contains the surface of the water, i.e. it is neither supported above the surface of the water nor submerged below the surface of the water.